The present invention relates to a low loss reflection-type analog phase shifter circuit producing nearly 360.degree. of phase shift at X-band. The inventive circuit experiences low insertion loss variation with phase. The circuit is implementable readily in a monolithic microwave integrated circuit (MMIC) using GaAs.
Analog phase shifters are well-known, as disclosed for example in U.S. Pat. No. 4,837,532 and 4,638,629. Such phase shifters using hyperabrupt varactor diodes also are known, as set forth in the paper by Niehenke et al., Linear Analog Hyerabrupt Varactor Diode Phase Shifters, 1985 IEEE MTT-S Digest, pp. 657-660. Such is also known from U.S. Pat. No. 4,638,269.
However, while such phase shifters are known, the results of these phase shifters at X-band have not demonstrated a full 360.degree. phase shift, and small insertion loss variation with phase. For example, the above-referenced paper discloses results of about 270.degree. of phase shift, and a total insertion loss modulation of 1.7 dB. The just-mentioned U.S. patent improving on results disclosed in a paper (Dawson et al.), An Analog X-Band Phase Shifter. IEEE 1984 Microwave and Millimeter-Wave Monolithic Circuits Symposium, Digest of Papers, pp. 6-10, shows about 180.degree. of phase shift, using serially-connected varactors for increasing phase shifter power handling capability. The paper itself showed only 105.degree. of phase shift, but the patent stated that the relatively poor results were due to limitations of tuning capacitance across the varactor diode pair in the fabricated chip.
Another paper, by Garver, 360.degree. Varactor Linear Phase Modulator, IEEE Transactions on Microwave Theory and Techniques, Vol. MTT-17, No. 3. March 1969, pp. 137-147, discloses the provision of 360.degree. modulation by combining two varactor diodes each providing 180.degree. modulation, in parallel. However, the parallel-coupled varactors are connected to a circulator, and not to a hybrid coupler. Further, the characteristic impedance of the Garver system is higher (50.OMEGA.) than that contemplated by the invention.